[TASK] Move page layout resolving into a separate class

The functionality "getData = pagelayout" resolves the
selected backend layout for the current page, which is
used in TypoScript quite frequently.

In order to use this in e.g. TypoScript conditions, this
functionality is now extracted into a separate class,
and multiple unit tests are added.

Resolves: #89655
Releases: master
Change-Id: I5f2af5ec692c0dd98712c8916a7dc2fed8836a95
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62306


Tested-by: Susanne Moog <look@susi.dev>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>